History and Background
Manual J is an internationally recognized standard, that was created and continues to be maintained by the Air Condition Contractors of America (ACCA), for estimating the heating and cooling loads (in Btu/h) of residential buildings. It was originally developed over 50 years ago and is currently on the 8th edition, version 2.5 (MJ8v2.5), last updated in 2016. It is intended to be used for estimating loads for these types of buildings:
Single-family-detached homes, duplex or triplex
Single-family-attached structures (row house, townhouse, etc)
Dwelling units in multi-family attached structures (condo and apartment units)
Manufactured homes
Procedure Overview
Homes lose and gain heat through three primary mechanisms:
Conduction, i.e. Heat transfer through surfaces like walls and windows
Convection, i.e. air infiltration through cracks in the building
Radiation, i.e. solar gains
The Manual J procedure specifies a process for measuring the geometry of buildings, making assumptions about building materials and specifies the required math to calculate:
Heating loads in the winter
Cooling loads in the summer
Sensible cooling
Latent cooling
Source: ACCA Manual J, MJ8
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